[47.01] The evolution of protostellar disks under the influence of external UV radiation and central stellar winds

The hydrodynamic evolution of protostellar disks under the
influence of external ultraviolet radiation and stellar
winds from their central stars is calculated numerically
with a 2D (rotational symmetry assumed), multigrid code. The
UV radiation alone results in the gradual photoevaporation
of the disk, characterized by a neutral disk wind (disk
material dissociatiated and heated by FUV radiation)
surrounded by an ionization front, where the outflowing disk
wind is ionized by EUV radiation. The overall appearance
resembles the cometary shape of "proplyds" seen in Orion,
NGC3603, and other star forming regions containing O stars.
When the disk's central star has a T Tauri type wind,
however, the shape and appearance will be modified. The
stellar wind, assumed to be initially isotropic, is focussed
into a bipolar outflow. Mixing of the stellar wind
containing no angular momentum with molecular material from
the inner disk regions, moving at Keplerian velocities,
results in an outflow that has too much angular momentum to
remain strongly focussed. Thus, the axial regions of the
outflow are depleted of material and the corresponding
temperatures are low due to adiabatic expansion. Most of the
outflowing material is concentrated in a conical shell, the
opening angle of which is determined by the parameters of
the disk wind.

This research is supported by NASA through grant
NRA-99-01-ATP-065 and by the DFG (Deutsche
Forschungsgemeinschaft).